October 7, 2002
12:00 AM (EDT)

News Release Number: STScI-2002-17

Hubble Spots an Icy World Far Beyond Pluto

October 7, 2002: NASA's Hubble Space Telescope has measured the largest object
discovered in the solar system since the discovery of Pluto
72 years ago. Approximately half the size of Pluto, the icy world is called "Quaoar" (pronounced kwa-whar). Quaoar is about 4 billion miles away, more than a billion miles farther than Pluto. Like Pluto, Quaoar dwells in the Kuiper belt, an icy belt of comet-like bodies extending 7 billion miles beyond Neptune's orbit.

Q & A: Understanding the Discovery

1.
How large is "Quaoar"?

Using Hubble's Advanced Camera for Surveys, astronomers determined that "Quaoar" has a diameter of about 800 miles (1300 kilometers). Hubble's observation is the first direct measurement of a Kuiper belt object's true size. Although astronomers have discovered 500 Kuiper belt objects over the past decade, they have estimated the sizes of only the largest of them. But astronomers could not measure the true sizes of the objects because they are small, dim, and far away.

2.
What is the significance of this finding?

This new object is the "biggest fish" astronomers have snagged in surveys of Kuiper belt objects. Astronomers theorize that even larger icy worlds reside in the Kuiper belt, a reservoir of material from the birth of our solar system. The Kuiper belt is a vast frontier where astronomers are just beginning to hunt for clues about the early solar system. Objects like "Quaoar" could help enlighten astronomers about the birth of our solar system planets.